He told BBC Radio 4's World at One that there would not only be Mr Huhne and Mr Clegg seeking to succeed him.

I like young Turks. I was a young Turk myself

Sir Menzies CampbellLib Dem leader

"Remember there are some women of talent around and some other men as well.

"When the runners and riders are finally declared at some unspecified time in the future, then there will be plenty of talent to choose from," he said.

Sir Menzies, who has said he will lead the party into the next election and into the next parliament, said there was no vacancy at the moment.

'Spring in step'

He added: "I like young Turks. I was a young Turk myself and that is why I have promoted young Turks - male and female - into the shadow cabinet."

However the speculation over his leadership has increased the pressure on Sir Menzies ahead of his keynote speech to the Lib Dem conference in Brighton on Thursday.

And it comes despite Sir Menzies getting a poll boost with an ICM survey suggesting he was more popular than Conservative leader David Cameron.

Mr Clegg: Heightened leadership talk

In an interview with the BBC's political editor Nick Robinson, he said: "Party leaders have always got to put in quite a speech - I remember it was true of Paddy Ashdown and of Charles Kennedy as well.

"But I intend to send the delegates home with a spring in their step, determined to take on Labour and the Conservatives as soon as an election is called."

He said only the Liberal Democrats could offer policies that would "change the face of Britain" while accusing Labour and the Conservatives of a "cosy consensus" on the environment, pensions and taxes.

'Straight answer'

Speaking at the Observer fringe event in Brighton on Tuesday, Mr Clegg urged the party to support Sir Menzies and "put two fingers up" at its critics.

But when asked to state his future intentions, Mr Clegg said: "If you are asking me would I stand against Ming, the answer is no".

When pushed on the issue, he responded that "if there was a vacancy in the future then I probably would".

I am not a sort of Michael Heseltine figure who plans their route map to Downing Street from the day they come out of nappies

Chris Huhne

On Wednesday he told BBC Two's Daily Politics he had given a "straight answer to a straight question" and he had spoken to Sir Menzies who said he was "very comfortable with what I had said".

But Mr Huhne said it was too early to talk about the succession.

He told the BBC: "There is no vacancy and it would be premature to even talk about the possibility as there is no vacancy.

"I am not a sort of Michael Heseltine figure who plans their route map to Downing Street from the day they come out of nappies. I wait for opportunities and decide at the time.

"I am very glad to be doing the environment brief which I think is the key challenge facing the country."

Poll advantage

The Guardian/ICM poll gave Sir Menzies a narrow advantage over Mr Cameron.

Some 36% of those taking part said they were satisfied with Sir Menzies and 41% dissatisfied - a net rating of minus five.

The survey suggests 37% of all voters are satisfied with the way Mr Cameron is doing his job, against 45% who are dissatisfied - a net satisfaction rating of minus eight.

The more coverage we get, the more people see of our ideas and our policies, the higher our poll rating goes

Ed DaveyLib Dem campaigns chief

By contrast, Prime Minister Gordon Brown enjoyed a comfortable satisfaction rating of plus 32, with 55% of all voters saying they are happy with the way he has performed since his arrival in 10 Downing Street in June, against 23% who say they are not.

The poll puts Labour support in a possible general election at 40% - up one point on a similar survey last month - with the Conservatives down two on 32% and the Lib Dems up two on 20%.

ICM questioned 1,005 adults by telephone between 13 and 16 September.

Lib Dem campaigns chief Ed Davey said the poll showed the party's message on the "environment and fairness" was getting through.

"The more coverage we get, the more people see of our ideas and our policies, the higher our poll rating goes. The reverse seems to happen with Tory leaders" Mr Davey told reporters.

Asked whether he had leadership ambitions of his own, he said "there is no vacancy".